The inventive subject matter relates to a device and method to control strain and tensile stress on thermal interface material in a heat spreader. More particularly, the inventive subject matter pertains to a device and method that determine stress points in thermal interface material used to transfer heat from a die to a heat spreader and design the heat spreader to optimize the thickness of thermal interface material for those stress points.
In the rapid development of computers many advancements have been seen in the areas of processor speed, throughput, communications, fault tolerance and size of individual components. Today""s microprocessors, memory and other chips have become faster and smaller. However, with the increase in speed, reduction in the size of components, and increased density of circuitry found within a given chip/die, heat generation and dissipation have become more critical factors than ever.
FIG. 1 illustrates a die 50 placed on a substrate 30 with a finite amount of a thermal interface material (TIM) 20 placed on top of the die 50. This TIM 20 serves at least two primary purposes. First, it acts to conduct heat from the die to the integrated heat spreader (IHS) 10. Second, it may also provide some adhesion between the IHS 10 and die 50. The TIM 20 may be composed of, but not be limited to, solder, a polymer containing metal, or some other substances which both act to transfer heat and provide some adhesion. During the manufacturing process the IHS 10 is pressed down upon the TIM 20 and adhesive 40, resulting in a structure as shown in FIG. 2.
As shown in FIG. 2, the IHS 10 would absorb heat from die 50 through TIM 20 and be held in place on the substrate 30 via adhesive 40. On top of the IHS 10 a heat sink (not shown) or fan/heat sink combination (not shown) would be mounted to dissipate the heat absorbed by the IHS 10. However, since IHS 10 and TIM 20 both experience significant tensile stress during the assembly process and due to thermal expansion and contraction when the die is powered on and off, as shown in FIG. 3, air gaps 60 form between the TIM 20 and IHS 10. As indicated in FIG. 3, these air gaps 60 may form at the outer edges of the TIM 20 while the center portion of the TIM 20 remains in contact with the IHS 10.
However, as shown in FIGS. 3 and 4, an air gap 60 may occur anywhere in the contact area between TIM 20 and IHS 10. As illustrated in FIG. 4, an air gap 60 may form in the center of the contact area between the TIM 20 and IHS 10, while the outer edges of the TIM 20 remain in contact with the IHS 10.
As would be appreciated by one of ordinary skill in the art, these air gaps 60 shown in FIGS. 3 and 4 may form anywhere in the contact area between the TIM 20 and IHS 10 depending on the materials utilized in the IHS 10 and TIM 20 as well as the handling procedures for the IHS 10 during the manufacturing process. Further, these air gaps 60 may also form in the TIM 20 itself. It should be noted that FIGS. 3 and 4, except for the inclusion of air gaps 60, remain unchanged from that shown in FIG. 2 and will not be discussed in further detail.
Since separation may occur between the TIM 20 and IHS 10, forming air gaps 60, as shown in FIGS. 3 and 4, due to thermal expansion and contraction, these air gaps 60 act as insulation, preventing heat being transferred from the die 50 to the IHS 10. As heat builds up in the die 50 to higher levels, the life expectancy of the die 50 is reduced.
Therefore, what are needed are a device and method that can determine the stress points between the TIM 20 and IHS 10 due to thermal expansion and contraction. Further, what are needed are a device and method that may compensate for the tensile and shear stress, thereby preventing the separation of the TIM 20 and the IHS 10. Still further, what are needed are a device and method that will provide for efficient heat transfer from the die 50 to the IHS 10.